The JWM Model 1152 Phase Locked Oscillator provides a very stable LO frequency source replacement for crystal-based oscillators used in the microwave bands. Its small size and low current consumption simplify integration into existing systems.

The DEMI series Transverters are a great way to get on the bands quickly. Complete kits eliminate the parts procurement phase that sometimes gets in the way of getting on the air quickly. However, there is room for improvement, especially in terms of frequency generation and control. The DEMI local oscillator (MICROLO), is a crystal-based unit putting out 1136MHz at approximately 3dBm to 5dBm. The Model 1152 simply replaces the MICROLO circuit board to eliminate the drift and frequency accuracy issues.

The documentation on the DEMI unit mentions that "more is better, less is not" when tuning the MICROLO board. The MICROLO output power at 1136MHz is on the order of +5dBm. This may mislead users of the Model 1152 unit into thinking that the 10-plus dBm output level is okay to inject into the DEMI Transverter board directly. But this is not the case.

First, users interfacing the Model 1152 to the DEMI Transverter should place some attenuation between the PLL output port and the LO input on the DEMI Transverter unit. To high of a LO power will introduce phase noise and distortion in the final output signal at 10368MHz.

Second, the Model 1152 unit requires a "clean" DC power source. Installing a simple pi-network filter will prevent troubles later. The filter components used are a pair of 200uF, 35V electrolytic capacitors and a coil (50T on a 1/2-in. Toroid core, not critical).

The Reference Oscillator (10MHz TCXO)

The user-supplied 10MHz Reference oscillator must be checked on an oscilloscope to verify output level, as mentioned in the manual. The surplus Qualcomm TCXO that I used generated at least 700mV p-p, so a 3dB pad made with 1/4 watt resistors was installed at the output of the TCXO unit. A very handy Attenuator utility program called QEXPAD is available for download from the W1GHZ Web site. The file name is QEXPAD.zip

Wayne Yoshida KH6WZ
E-mail: kh6wz@arrl.net